First off I want to thank Keith Barker for teaching IPv6. You’ve been instrumental in helping me understand IPv6 and how it’s similar and different from IPv4. This post was written as a journey of me going over the class information.

What is an IPv6 Address?

Keith talks about IPv6 and how it is similar to house addresses. The two main parts of an address are:

Street Name – Represents the Network address in IPv6. The network Address is called the “Network Prefix” and tells us about the network groupings of computers.

House Address – Represents a single device in IPv6. It is called the “Interface Identifier”.

What does an IPv6 Address look like?

A IPv6 address has several qualities:

IPv6 address are 128bits in length.

A mask is essentially the dividing line between the network address called the “Network Prefix” and the host address called the “Interface Identifier”.

A Mask of /64 following the address will mean that the Network Address is 64bit and the Host Address is 64bits.

Most addresses will have a mask of /64

Each IPv6 address scan be broken down into 8 groups of 16bits each.

Each group is separated by semi-colons.

Every 4bits can be converted into a single Hex character. People some times call 4bits a nibble since it’s half of a byte.

All leading Zeros can be dropped from the group. More on this near the end of the post.

2 or more groups of consecutive zeros can be merged by putting a :: and then a zero. This can only be done once. More on this near the end of the post.

Before looking at what an IPv6 address normally looks like… it is a good idea to look at what the address looks like in binary:

*Note* – There is no spaces and the address should be all on one line. Due to the size of the address had to fit it on two lines.

How to convert from Binary to Hex.

It’s probably best that you first start off by looking at this Hex Cheat Sheet.

After looking at the Hex cheat sheet you are probably starting to understand why I said in the previous section 4bits can be converted into a Hex character. Using the cheat sheet let’s convert the binary address into the Hexadecimal address that we’ll actually work with on routers and devices.

I’ll break the process up over each 16bits.

Let’s work on the Network Prefix:

0010000000000001:0000110110111000:0000000000100001:0000000100010001

0010 0000 0000 0001 – This equals “2001” in hex.

0000 1101 1011 1000 – This equals “0DB8” in hex.

0000 0000 0010 0001 – This equals “0021” in hex.

0000 0001 0001 0001 – This equals “0111” in hex.

We now know the network prefix is: “2001:0DB8:0021:0111”

Let’s work on the Interface Identifier:

0010000010000001:0000110110101000:0000100000100001:0000000101010001

0010 0000 1000 0001 – This equals “2081” in hex.

0000 1101 1010 1000 – This equals “0DA8” in hex.

0000 1000 0010 0001 – This equals “0821” in hex.

0000 0001 0101 0001 – This equals “0151” in hex.

This is how the Full IP address will look like in Hex:

2001:0DB8:0021:0111:2081:0DA8:0821:0151/64

Ok. Now that you’ve seen what an IPv6 address looks like… check out the IPv6 cheat sheet:

Let’s take a look at what IPv6 will look like on Cisco IOS. This is the output from setting up an IPv6. Notice the leading zeros had been removed.

You might be wondering 6 things about the line that says: FE80::2D0:BCFF:FE20:7802

What is this called? This is a IPv6 Link Local Address

How was it entered? – The router “auto-magically” created this address.

What is the “::” mean? – This means that several groups of zeros have been shrunk down to shorten the address.

Why do some of the groups only have less than 4 characters. – This means that there were leading zeros and were dropped.

Is there something special about “FE80”? – Yes. This means this address is a link local address.

How did the Interface Identifier get created? – It was created using the MAC address of the device it was assigned to.

I hope I’ve wet your appetite enough to want to learn All About IPv6 Link Local Addresses

First what is the OSI model? The OSI model is a framework of protocols that allows two devices to communicate on a network or over the internet. Each layer of the OSI model makes each layer responsible for over looking and carrying out a specific task. I’ve made a cheat sheet that breaks everything down into it’s most basic form. I will be referring to this chart throughout the rest of this post.

The OSI layer is broken up into 7 layers. The top most layer is layer 7 and the lowest layer is Layer 1. Each layer has been given a name that helps identify what is happening on each layer.

Let’s go over the OSI Layer in more detail

Layer 7 is the Application layer. This is the layer that us a humans interact with the most. This layer the application sets up rules on how an application will send and receive data. Much like Languages, if both people don’t speak the same one, a conversation will not likely amount to anything.

Layer 6 is is the Presentation layer. It helps the Application layer by formatting the data in such a way that both parties will be able to read it.

Layer 5 is the Session layer. It helps ensure that the data is synchronized.

Layer 4 is the Transport layer. It is responsible for creating and managing the packets that will go out on the network.

Layer 3 is the Network layer. It is responsible for Addressing and Routing. This layer is in charge of the IP address of the hosts as well as knowing how to route information to another host. Because IP supports routing the destination host can be local or out the internet.

Layer 2 is the data link layer. It is responsible for Data frames and the Management of those frames. Data frames deal with layer 2 addresses (MAC Address) which are non-routable addresses. Technically Layer 2 can actually be broken up into two sub-layers:

Logical Link Control

Media Access Control (NIC’s Mac Address)

Layer 1 is the Physical Layer. It is responsible for talking with a physical device like a NIC. In particular it’s changing the data into electronic pulses that can be sent out on the wire.

Device Type by Layer

To give you a better idea what layers the network devices work at I created the device type column.

Layer 7 – I put gateway here. This is not the same as a “Default Gateway”. This is a device that works kind of like a translator. It is able to understand application languages like HTTP, SMTP, etc. The term “Next Generation Firewalls” is some times applied to these devices.

Layer 3 – Routers and “Swouters” devices go here. A Swouter is a layer 3 switch. It has more than a couple ports on the back and is capable of routing.

Layer 2 – This is the typical layer where switches are put. Switches are able to look at traffic and filter data based on MAC addresses.

Layer 1 – Typically Hubs and Repeaters are put here. You don’t really see them anymore because they tend to be slow and pretty brain dead. Because of this they only work “well” in a very small network design.

TCP/IP Model

You will notice that the TCP/IP model only has 4 layers. The four layers correlate to one or more of the OSI Model. Later versions have 5 and have different names. From what I’ve read we need to know both.

TCP/IP Stands for Transmission Control Protocol/Internet Protocol. It is the basic communication protocol of the Internet. It can be used on the internet as well as private networks. TCP/IP is based off the 4 layer Darpa model. Looking back at the “Cheat sheet” you will notice that I’ve filled in a column with what protocols are used at each layer.

Transmission Protocols

There are two types of transmission protocol types in TCP/IP. These protocols are called TCP and UDP. TCP is like Certified Mail and UDP is like 1st class Mail. Only Certified mail tells you if the other side has received all packages.

TCP (Transmission Control Protocol)

One to One

Connection Oriented

Reliable Communication

UDP (User Datagram Protocol)

Multicast (one to many)

Connectionless

Unreliable

Connection orientated communication means that connection must be established before data can be exchanged. TCP uses a three-way handshake to establish this connection.

I want to thank Wendell Odem for posting the video. He did an amazing job of explaining the setup of the network but didn’t actually go through all the commands. This post tries to compliment the free training he did with Cisco press.

I will be using Packet Tracer 6.0.1.011 for setting up the network he talks about.

I bet you are wanting to learn about how to reset a cisco router so that all the settings have been cleared. Well you are at the right place!

You can use config-register 0x2102 command to reset a Cisco router back to Factory Defaults.

Note: to check the configuration register on the router by issuing the show version command. The configuration register setting is displayed in the last line of the show version command output, and should be set to 0x2102.

This is example how to reset a Cisco router back to Factory Defaults:

Router1#conf tEnter configuration commands, one per line. End with CNTL/Z.

TCP/IP and OSI Network Model

A network model refers to a comprehensive set of documents that define how a network should work

Protocols are a set of logical rules that devices must follow to communicate

Physical requirements for networking define the voltage and current levels used on a cable when transmitting.

Main networking models

There are two main networking models that people refer to when talking about networking models

OSI – Ended up “loosing” the race but we almost always use it’s layers when describing networking functions. It was made by the “International Organization for Standardization”.

TCP/IP – Ended up “becoming” the standard that every single computer, tablet and phone now uses. It was made at Universities for a DoD contract.

Overview of the TCP/IP Networking Model

TCP/IP (like OSI) both DEFINES and REFERENCES a large collection of protocols. The protocols allow devices like computers to communicate.

To define a protocol, TCP/IP uses documents called Requests for Comments (RFC)

To avoid repeating work, it will sometimes refer to standards or protocols created by other groups

IEEE Defined Ethernet LANS

TCP/IP does not define Ethernet in a RFC, rather it refers to IEEE Ethernet as an option

Each Layer includes protocols & standards that relate to that category of functions

TCP/IP Protocols and Examples

This isn’t an exhaustive list by any means…

Application – HTTP, POP3, SMTP

Transport – TCP/UDP

Internet – IP

Link – Ethernet, PPP, T1, T3

TCP/IP Application Layer

Provides services to the application software running on a computer

Application layer does NOT define the application itself. Rather it defines the services that the application needs. Eg. There are many Web browser application on the market. Internet Explorer, Firefox, Safari and Chrome. The Application layer does NOT define these applications. It defines how web servers and web browsers talk to each other.

Basic HTTP Logic

Let’s go over the diagram above:

1.) HTTP header gets sent. The header includes a “GET” message. If there is no file in particular the web server will assume the computer is asking for the default webpage

2.) The message returns a return code (200) which means “OK”. The second message includes the first part of the requested file.

3.) Another message gets sent, but this time without a HTTP header. HTTP transfers data by sending multiple messages.

*NOTE* – HTTP won’t waste space by sending repeated HTTP headers!

TCP/IP Transport Layer

Transport Layer includes a smaller # of protocols than the application layer

Two most common protocols are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)